Shaker and degasser combination

ABSTRACT

A system for separating components from a slurry of drilling fluid and drill cuttings on a shaker screen having an upper side and a lower side within a shaker. The system also has a pressure differential generator to pull an effective volume of air through a section of the shaker screen to enhance the flow of drilling fluid through the section of the shaker screen and the separation of drilling fluid from drill cuttings and further maintain an effective flow of drill cuttings off the shaker. A method of separating components of a slurry of drilling fluids and solids has the steps of delivering the slurry to a shaker, flowing the slurry over a first screen and applying an effective amount of vacuum to a first portion of the first screen to remove the drilling fluids from the slurry without stalling the solids on the first screen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patent application Ser. No. 13/845,704 which claims benefit to U.S. patent application Ser. No. 11/862,955, filed Sep. 27, 2007, which claims benefit to U.S. Provisional Patent Application No. 60/827,567, filed Sep. 29, 2006, and U.S. Provisional Patent Application No. 60/827,542, filed Sep. 29, 2006. The disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments disclosed herein relate generally to shale shakers and screens for shale shakers. Specifically, embodiments disclosed herein relate to a shale shaker having pulse-vacuum assisted screening. Additionally, embodiments disclosed herein relate to methods and apparatus for removing entrained gases from a slurry.

Oilfield drilling fluid, often called “mud,” serves multiple purposes in the industry. Among its many functions, the drilling mud acts as a lubricant to cool rotary drill bits and facilitate faster cutting rates. The mud is mixed at the surface and pumped downhole through a bore of the drill string to the drill bit where it exits through various nozzles and ports, lubricating and cooling the drill bit. After exiting through the nozzles, the “spent” fluid returns to the surface through an annulus formed between the drillstring and the drilled wellbore.

Furthermore, drilling mud provides a column of hydrostatic pressure, or head, to prevent “blowout” of the well being drilled. This hydrostatic pressure offsets formation pressures thereby preventing fluids from blowing out if pressurized deposits in the formation are breeched. Two factors contributing to the hydrostatic pressure of the drilling mud column are the height (or depth) of the column (i.e., the vertical distance from the surface to the bottom of the wellbore) and the density (or its inverse, specific gravity) of the fluid used. Various weighting and lubrication agents are mixed into the drilling mud to obtain the right mixture for the type and construction of the formation to be drilled. Increasing the amount of weighting agent solute dissolved in the mud base will generally create a heavier drilling mud. Drilling mud that is too light may not protect the formation from blowouts, and drilling mud that is too heavy may over invade the formation. Therefore, much time and consideration is spent to ensure the mud mixture is optimal. Because the mud evaluation and mixture process is time consuming and expensive, drillers and service companies prefer to reclaim the returned drilling mud and recycle it for continued use.

Another significant purpose of the drilling mud is to carry the cuttings away from the drill bit to the surface. As a drill bit pulverizes or scrapes the rock formation at the bottom of the borehole, small pieces of solid material are left behind. The drilling fluid exiting the nozzles at the bit stir up and carry the solid particles of rock and formation to the surface within the annulus between the drillstring and the borehole. Therefore, the fluid exiting the borehole from the annulus is a slurry of formation cuttings in drilling mud, and the cutting particulates must be removed before the mud can be recycled.

One type of apparatus used to remove cuttings and other solid particulates from drilling mud is commonly referred to in the industry as a “shale shaker.” A shale shaker, also known as a vibratory separator, is a vibrating sieve-like table upon which returning used drilling mud is deposited and through which substantially cleaner drilling mud emerges. Typically, the shale shaker is an angled table with a generally perforated filter screen bottom. Returning drilling mud is deposited at the top of the shale shaker. As the drilling mud travels down the incline toward the lower end, the fluid falls through the perforations to a reservoir below thereby leaving the solid particulate material behind. The combination of the angle of inclination with the vibrating action of the shale shaker table enables the solid particles left behind to flow until they fall off the lower end of the shaker table. The above described apparatus is illustrative of one type of shale shaker known to those of ordinary skill in the art. In alternate shale shakers, the top edge of the shaker may be relatively closer to the ground than the lower end. In such shale shakers, the angle of inclination may require the movement of particulates in a generally upward direction. In still other shale shakers, the table may not be angled, thus the vibrating action of the shaker alone may enable particle/fluid separation. Regardless, table inclination and/or design variations of existing shale shakers should not be considered a limitation of the present disclosure.

Preferably, the amount of vibration and the angle of inclination of the shale shaker table are adjustable to accommodate various drilling mud flow rates and particulate percentages in the drilling mud. After the fluid passes through the perforated bottom of the shale shaker, it may either return to service in the borehole immediately, be stored for measurement and evaluation, or pass through an additional piece of equipment (e.g., a drying shaker, a centrifuge, or a smaller sized shale shaker) to remove smaller cuttings and/or particulate matter.

Screens used with shale shakers are typically emplaced in a generally horizontal fashion on a generally horizontal bed or support within a basket in the shaker. The screens themselves may be flat or nearly flat, corrugated, depressed, or contain raised surfaces. The basket in which the screens are mounted may be inclined towards a discharge end of the shale shaker. The shale shaker imparts a rapidly reciprocating motion to the basket and hence the screens. Material from which particles are to be separated is poured onto a back end of the vibrating screen, flowing toward the discharge end of the basket. Large particles that are unable to move through the screen remain on top of the screen and move toward the discharge end of the basket where they are collected. The smaller particles and fluid flow through the screen and collect in a bed, receptacle, sump, or pan beneath the screen.

In some shale shakers a fine screen cloth is used with the vibrating screen. The screen may have two or more overlaying layers of screen cloth or mesh. Layers of cloth or mesh may be bonded together and placed over a support, supports, or a perforated or apertured plate. The frame of the vibrating screen is resiliently suspended or mounted upon a support and is caused to vibrate by a vibrating mechanism (e.g., an unbalanced weight on a rotating shaft connected to the frame). Each screen may be vibrated by vibratory equipment to create a flow of trapped solids on top surfaces of the screen for removal and disposal of solids. The fineness or coarseness of the mesh of a screen may vary depending upon mud flow rate and the size of the solids to be removed.

While there are numerous styles and sizes of filter screens, they generally follow similar design. Typically, filter screens include a perforated plate base upon which a wire mesh, or other perforated filter overlay, is positioned. The perforated plate base generally provides structural support and allows the passage of fluids therethrough, while the wire mesh overlay defines the largest solid particle capable of passing therethrough. While many perforated plate bases are generally flat or slightly curved in shape, it should be understood that perforated plate bases having a plurality of corrugated or pyramid-shaped channels extending thereacross may be used instead. In theory, the pyramid-shaped channels provide additional surface area for the fluid-solid separation process to take place, and act to guide solids along their length toward the end of the shale shaker from where they are disposed.

The separation of drilling fluid and other solids from drill cuttings using a screen shaker is often incomplete, resulting in wet drill cuttings. As described above, the drilling mud is introduced to the top of the screen and allowed to flow downward through the screen by gravity alone. Often, additional equipment, such as additional screen separators, hydro cyclones, dryers, drying shakers, centrifuges, hydro cyclone shakers, thermal desorption systems, and other equipment, are used to further dry the cuttings and recover drilling fluid. For example, cuttings from a shale shaker may fall onto a rotary vacuum dryer, where the cuttings travel on a circumferentially rotating screen. Air may be used to strip drilling fluid off the cuttings and into the screen, such as by pulling a vacuum from the interior of the rotating screen (for example, the ROTAVAC™ Rotary Vacuum Dryer fluid recovery and cuttings drying system, available from Halliburton).

It is desired to improve the rate and efficiency at which shakers remove liquid from cuttings or other solids. To enhance the gravity-driven separation as described above, it is known that increasing the head on the shaker can increase the throughput of fluids through the screen. Increasing the pressure differential through the screen will likewise increase the fluid capacity of the shaker.

One example of a shaker with increased pressure differential is disclosed by Hensley et al. in U.S. Patent Application Publication No. 20050183994A1. Hensley et al. disclose an integrated, transportable cutting treatment system, where a pressure differential is developed across the screens to increase the flow rate of drilling mud through the screens. Hensley et al. use an air pump to develop a vacuum beneath the screens to draw mud through the screens. However, applying a continuous vacuum beneath a screen to draw fluid through the screen may result in solids sticking to the screen, hindering the conveyance of solids off the end of the shaker as needed, thereby preventing fluids from being filtered through the screen.

There exists a continuing desire for shakers having increased fluid capacity, increased fluid flow-through rates across the screens, and/or improved fluid removal efficiencies. Accordingly, there exists a need for a shaker with increased pressure differential. Preferably, the means used to increase the pressure differential do not substantially hinder the flow of solids across the screen deck. Additionally, there exists a need for a shaker for removing entrained gases from the recovered drilling fluid.

SUMMARY OF THE INVENTION

A system for separating components of a slurry is disclosed, the system including a housing; a basket for holding at least one shaker screen, the basket movably mounted in the housing; at least one vibrator coupled to the basket; a sump disposed below the basket to collect at least a portion of the slurry passing through the at least one shaker screen; a pressure differential device fluidly connected to the sump for developing a pressure differential across the at least one shaker screen; and a toggling device for toggling the pressure differential across the screen. In some embodiments, the vapor may be degassed within the sump. In other embodiments, the system may include a degassing chamber fluidly connected to the sump and the pressure differential device, wherein the degassing chamber is disposed between the sump and the pressure differential device; and a fluid conduit fluidly connected to the degassing chamber for recovering a degassed fluid.

In another aspect, embodiments disclosed herein relate to a method for separating components of a slurry, the method including providing a slurry to a top of a screen and toggling a pressure differential across the screen from static to a vacuum below the screen. In some embodiments, the toggling may include generating at least a partial vacuum below the screen by causing a flow of vapor from a vapor space below the screen, and intermittently interrupting the vacuum by disrupting the flow of vapor. In other embodiments, the partial vacuum may be generated by causing a flow of fluid from a space below the screen, the fluid may be degassed to recover a vapor and a degassed liquid, and the toggling may be performed by intermittently interrupting the vacuum by disrupting the flow of recovered vapor.

In an aspect of the invention, a method of separating components of a slurry of drilling fluids and solids is provided. The method has the steps of delivering the slurry to a shaker; flowing the slurry over a first screen; and applying an effective amount of vacuum to a first portion of the first screen to remove the drilling fluids from the slurry without stalling the solids on the first screen.

In an embodiment, the method has the step of intermittently interrupting and/or pulsing the amount of vacuum applied to the first screen.

In an embodiment, the method has the step of controlling the air flow under the screen to prevent stalling of drill cuttings in the slurry on the screen.

In an embodiment, the method has a step of applying a vacuum force to the shaker screen sufficient to effectively reduce drilling fluid retained on cuttings in the slurry to a level below that obtained when no vacuum force is applied.

In another aspect of the invention, a system for separating components from a slurry of drilling fluid and drill cuttings on a shaker is provided. The system has a shaker screen having an upper side and a lower side for separating drill cuttings and drilling fluid within a shaker. The system also has a pressure differential generator to pull an effective volume of air through a section of the shaker screen to enhance the flow of drilling fluid through the section of the shaker screen and the separation of drilling fluid from drill cuttings and further maintain an effective flow of drill cuttings off the shaker.

In an embodiment, the system has a toggling device to alternate a pressure differential below the section of the shaker screen from zero vacuum to at least a partial vacuum.

In an embodiment, the effective volume of air pulled through the screen is adjustable to prevent stalling of drill cuttings in the slurry on the screen. In another embodiment, the system has a plurality of shaker screens wherein the pressure differential generator pulls an effective volume of air through a section of the screens.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a vibratory screen separator useful in embodiments disclosed herein.

FIG. 2 is a cross-sectional view of the screen separator of FIG. 1.

FIG. 3 is a side view of a vibratory screen separator useful in embodiments disclosed herein, where the separator may be fluidly attached to a vacuum system.

FIG. 4 is a perspective view of a vibratory screen separator frame and sump useful in embodiments disclosed herein.

FIG. 5 is a simplified flow diagram for embodiments of a system for generating a pressure differential across a screen and degassing a fluid according to embodiments disclosed herein.

FIG. 6 is a simplified flow diagram for embodiments of a system for generating a pressure differential across a screen and degassing a fluid according to embodiments disclosed herein.

FIG. 7 is a perspective view of a vibratory screen separator having a vacuum fume extraction device in accordance with embodiments disclosed herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one aspect, embodiments disclosed herein relate to a method for separating components of a slurry. As used herein, a slurry refers to a mixture of drilling fluid and drill cuttings. A slurry may be separated using a screen separator having a pressure differential across the screen. In other aspects, embodiments disclosed herein relate to a system for separating components of a slurry. The system may include, in some embodiments, a vibratory screen separator and a pressure differential device or a vacuum generating device. The pressure differential device may additionally provide a driving force to degas the recovered drilling fluid.

FIGS. 1 and 2 illustrate one embodiment of a vibratory screen separator. The separator 5 includes a base 10 having four legs 12 and supporting members 14. Mounted on the four legs 12 are resilient mounts 16. Each mount 16 includes a spring 18, a base 20 on each leg and a socket 22 on the separator to receive each spring 18. Positioned on the base 10 by the resilient mounts 16 is a separator frame or basket 24. The basket 24, includes sidewalls 26 and 28 and a back wall 30. The front side, opposite to the back wall 30, may be left open. The basket 24 is of sufficient structure to withstand the vibrational loads imposed on the basket 24 in operation. Extending across the interior of the basket 24 between the sidewalls 26 and 28 is a structural tube 32 which may be positioned at roughly the center of mass for further structural strength.

Located about the sidewalls 26 and 28 and the back wall 30 is a channel 34. Located above the channel 34 on the sidewalls 26 and 28 are stops 38 and 40. The stops cooperate with the channel 34 through its extent along the sidewalls 26 and 28 to form a screen mounting in a first plane. A screen 42 having a screen frame 44 and screen cloth 46 is illustrated positioned in the screen mounting. Resilient members 48 are positioned on the underside of the stops 38 and 40 to help locate, seat and seal the screen frame 44. Obviously, multiple screens 42 may be employed in anyone separator.

A sump 50 is located below the screen mounting to receive material passed through the screen 42. An inlet 52 is positioned at the back wall 30 above the screen mounting. An outlet 54 for material passed through the screen 42 receives material from the sump 50 for discharge. Material not passing through the screen 42 is discharged off the end of the screen 42 and suitably collected. The flow across the screen plane from the inlet 52 toward the outlet 54 defines a linear direction of material travel. Attached to the sides of the basket 24 and specifically to each sidewall 26 and 28 are two rotary eccentric vibrators 56 and 58.

As illustrated in FIGS. 1 and 2, sump 50 may be integrally connected to basket 24. Thus, sump 50 may be referred to as a vibrating sump. In other embodiments, sump 50 may be separate from basket 24, a stationary sump.

A pressure differential device (not shown) may be provided to create a pressure differential between the vapor space above screen and the vapor space between screen 42 and sump 50. In some embodiments, the pressure differential device may be located internal to sump 50, such as an air pump (not shown). In other embodiments, the pressure differential device may be located external to sump 50, such as a vacuum system (not shown). Whether internal or external to sump 50, the pressure differential device may cause vapor to flow from the vapor space between screen 42 and sump 50 to a point external to sump 50, such as through outlet 54 or other conduits forming an outlet from sump 50.

The pressure differential device may include, in some embodiments, pumps, blowers, aspirators, ejectors, and the like, and combinations thereof. In various embodiments, the pressure differential may be created by one or more of a positive displacement pump, a momentum transfer pump, or an entrapment pump.

Pumps useful in creating the pressure differential or vacuum m some embodiments include reciprocating pumps, centrifugal pumps, vacuum pumps, pneumatic pumps, electric pumps, air pumps, piston pumps, rotary piston pumps, rotary vane pumps, screw pumps, scroll pumps, liquid ring pumps, external vane pumps, Wankel pumps, Toepler pumps, and Venturi vacuum pumps, among others. Blowers useful in creating the pressure differential may include booster pumps, a rotary lobe blower (such as a ROOTS™ blower), and vacuum blowers. Useful ejectors and aspirators may include steam ejectors, water aspirators, or ejectors and aspirators utilizing other motive fluids. In some embodiments, drilling fluid is used as the motive fluid for an ejector or an aspirator.

In some embodiments, the pressure differential may be pulsed, toggled, or intermittently interrupted. Toggling or pulsing of the pressure differential, as used herein, refers to the changing of the pressure differential from static (a zero pressure differential across the screen) to at least a partial vacuum below the screen. In some embodiments, the pressure differential may be toggled from static to at least a partial vacuum. In other embodiments, the pressure differential across a screen may be toggled or pulsed from static to a full vacuum below the screen. In some embodiments, the pressure differential may be toggled from static to a pressure differential in the range from about −0.1 to about −1.0 bar, as given by a quantity defined as a pressure below the screen minus a pressure above the screen. In other embodiments, the pressure differential may be toggled from static to a pressure differential in the range from about −0.2 to about −0.7 bar, as given by a quantity defined as a pressure below the screen minus a pressure above the screen; from static to a pressure differential in the range from about −0.2 to about −0.7 bar in other embodiments; and from about −0.3 bar to about −0.6 bar in yet other embodiments. By toggling the pressure between vacuum and static, conveyance of solids across the screen may proceed unhindered, thereby avoiding solids accumulating or sticking on the screen, and thus not preventing fluid flow through the screen.

Pulsing or toggling the pressure differential between static and vacuum below the screen, in some embodiments, may be effectuated by a valve disposed between the pressure differential device (pumps, ejectors, etc., as described above) and the screen. Manipulating the valve by opening and/or closing the valve, at least partially, may disrupt the flow of vapor from the sump, thereby affecting the pressure differential. In other embodiments, the toggling device, such as a valve, may be disposed between a vacuum generating device or system and the sump located under one or more of the screens.

Valves useful for toggling the pressure differential may include rotary valves, ball valves, globe valves, needle valves, butterfly valves, gate valves, plug valves, diaphragm valves, and piston valves, among others. The valves may be manually operated in some embodiments, or may be remotely actuated valves in other embodiments.

In some embodiments of the pulsed-vacuum assisted screening device disclosed herein, the separator may include two or more screens. One or more sumps may be located under the screens such that a pressure differential may be provided across less than all of the two or more shaker screens. In other embodiments, the same or different pressure differentials may be provided across zoned shaker screens.

FIG. 3 illustrates one embodiment of a pulsed-vacuum assisted screening device having separate pressure zones, where like numerals represent like parts. Separator 60 may include two or more screens (not shown), correspondingly located above two or more sumps 50 (i.e., 50A and SOB as illustrated). For example, where separator 60 has four screens in series, sump 50A may be located proximate inlet 52 under the first two screens. Sump SOB may be located proximate outlet 54B, under the last two screens (where first and last corresponds to the direction of flow from inlet 52 to outlet 54B). Sump 50A may thus create an independent zone from sump 50B, allowing for operations of the two zones at the same or different pressure differentials. One or more devices may be provided to create a pressure differential across either or both sets of screens. The pressure differential across the screens in either zone may be manipulated to provide additional capacity or to enhance the liquid recovery, resulting in a dryer cutting fraction. To maintain separate pressure differentials, sumps 50A and 50B may not be in fluid communication. As such, outlet 54A may be provided to discharge material passing through the first two screens into sump 50A.

As described above, one or more pressure differential devices may be provided to create a pressure differential between the vapor space above the screens and the vapor space between the screens and sumps 50A, 50B. In some embodiments, the pressure differential devices may be located internal to sumps 50A, 50B. In other embodiments, the pressure differential devices may be located external to sumps 50A, 50B. Whether internal or external to sumps 50A, 50B, the pressure differential devices may cause vapor to flow from the vapor space between the screen and sump 50A, SOB to a point external to each sump 50A, 50B, such as through outlets 54A, 54B, or other conduits forming an outlet from sumps 50A, 50B.

For example, outlet 54A may be used as a liquid outlet, discharging the drilling fluid and other solids passing through screens. An outlet 56A may be provided to convey vapor from sump 50A to create the desired pressure differential. Outlet 56A, in some embodiments, may be connected to a lobe pump 58 or to one or more vacuum generating devices as described above. The vapor discharge from vacuum generating device 58 may then be vented or further processed, such as through a vapor recovery or incineration system 59.

FIG. 4 illustrates another embodiment of the pulsed-vacuum assisted screening device. The separator may include a base, legs, supporting members, and other component parts as previously illustrated for mounting separator frame 74. Separator frame 74 may include sidewalls 76, 78 and a back wall 80. The front side 81, opposite to the back wall 80, may be left open. The frame 74 may be of sufficient structure to withstand the vibrational loads imposed on the frame 74. Extending across the interior of the frame 74 between the sidewalls 76, 78 may be a structural tube 82 which may be positioned at roughly the center of mass, for further structural strength.

Located about the sidewalls 76 and 78 and the back wall 80 is a channel (not shown). Located above the channel on the sidewalls 76 and 78 are stops 88 and 90. The stops cooperate with the channel (not shown) through its extent along the sidewalls 76 and 78 to form a screen mounting in a first plane. A screen 92 is illustrated positioned in the screen mounting. Multiple screens 92 may be employed in anyone separator.

One or more shaker screens 92 may be installed in, or secured to, the shale shaker frame 74 with a wedge block 94. The screen 92 is placed on a support rail (not shown) and positioned underneath a stationary wedge guide 88 (stop 88). The wedge block 90 (stop 90) is then pounded into position so as to secure the screens 92 to frame 74. One of ordinary skill in the art will appreciate that the operator often chooses to use a combination of a hammer and a suitable piece of wood in contact with the wedge block 90 to deliver sufficient force to fully tighten the wedge block 90. As shown in FIG. 4, the wedge block 90 may also include a hammer surface 94 to aid in installation (as by pounding on surface 94 a) and removal (as by pounding on surface 94 b).

An inlet (not shown) may be located proximate back wall 80. The solids may then travel on top of the screens toward front side 81. As illustrated, the separator has four screens 92. The drilling mud may be deposited on the first screen 92A. A sump 96 may be provided under the first two screens 92A, 92B. As illustrated, sump 96 may be integrally formed with frame 74. One or more pressure differential devices, as described above, may be provided to generate a pressure differential across screens 92A, 92B. An outlet 98 may be provided to convey vapor from sump 96 to create the desired pressure differential.

Referring now to FIG. 5, a simplified flow diagram for embodiments of a system for generating a pressure differential across a screen and degassing a fluid, according to embodiments disclosed herein, is illustrated. A shaker 100 may include a basket 102, shaker screen 104, and sump 106, as described above. A drilling fluid 108 to be separated, such as a mixture of drilling mud and drill cuttings, may be fed to inlet end A of the shaker 100. Drill cuttings separated from drilling fluid 108 may be recovered at outlet end B. The drilling mud 110 separated from the drill cuttings may be collected in sump 106.

To generate the desired intermittent pressure differential across screen 104, the vapor space 112 of sump 106 may be fluidly connected via flow line 113 to a valve 114 and a pressure differential device 116, as described above. To prevent liquids from entering flow line 113 and pressure differential device 116, vacuum system inlet 118 may be disposed vertically downward, may include a cover 120, such as to direct fluid away from inlet 118, or may include other safety devices to prevent fluid from entering the vapor system.

Vapors recovered via pressure differential device 116 may be flared, vented, or recovered via flow line 122. Fluids 110 may be recovered from sump 106 via flow line 124, and in some embodiments may be directed to a mud tank for further processing and/or recycled to the mud system.

In the embodiment illustrated in FIG. 5, the fluid 110 collecting in sump 106 during the separations may be degassed or partially degassed by the vacuum or partial vacuum generated by pressure differential device 116. Operation of pressure differential device 116 results in at least a partial vacuum in sump 106, and may provide a driving force for gases that may be dissolved or entrained in the fluid 110 to be separated therefrom.

If necessary, a vent 126 may be provided to aid in pressure control of sump 106 or to provide means to avoid under-pressure of sump 106, where vent 126 may include pressure relief valves and other devices known in the art to provide flow in limited circumstances.

Referring now to FIG. 6, a simplified flow diagram for embodiments of a system for generating a pressure differential across a screen and degassing the recovered fluid, according to embodiments disclosed herein, is illustrated. A shaker 200 may include a basket 202, shaker screen 204, and sump 206, as described above. A drilling fluid 208 to be separated, such as a mixture of drilling mud and drill cuttings, may be fed to inlet end A of the shaker 200. Drill cuttings separated from drilling fluid 208 may be recovered at outlet end B. The drilling mud 210 separated from the drill cuttings may be collected in sump 206.

To generate the desired intermittent pressure differential across screen 204, sump 206 may be fluidly connected via flow line 213 to a degassing chamber 212, valve 214, and a pressure differential device 216, as described above. Generation of the intermittent pressure differential across screen 204 results in both liquids and vapors being pulled from sump 206 to degassing chamber 212. The vapors collecting in degassing chamber 212 may be recovered via flow line 217, and may be flared, vented, or otherwise recovered via flow line 222. Fluids 210 collecting in degassing chamber 212 may be recovered via flow line 224, and in some embodiments may be directed to a mud tank for further processing and/or recycling to the mud system. If necessary, a vent 226 may be provided to aid in pressure control of degassing chamber 212, where vent 226 may include pressure relief valves and other devices known in the art to provide flow in limited circumstances.

The fluid 210 collecting in degassing chamber 212 during the separation process may be degassed or partially degassed by the vacuum or partial vacuum generated by the pressure differential device 216. Operation of pressure differential device 216 results in at least a partial vacuum in degassing chamber 212, and may provide a driving force for gases that may be dissolved or entrained to be separated from the fluid 210. Such degassing that may occur in embodiments described herein may allow for a simplified mud tank system, where vents and other degassing equipment may not be necessary.

As described above, shaker systems described herein may include a pressure differential device or vacuum generating device to generate an intermittent pressure differential across a shaker screen. The vacuum generated by the pressure differential device may provide an additional driving force for separating fluids from drill cuttings, and may additionally remove vapors and entrained gases from the filtered drilling fluid.

Referring now to FIG. 7, a perspective view of a vibratory separator 500 in accordance with an embodiment of the present disclosure is shown. In this embodiment, vibratory separator 500 includes a housing 502, a drilling fluid inlet end 504, an outlet end 506, and a plurality shaker screens 508. In the embodiment shown, the plurality of shaker screens 508 are assembled in a multi-tier configuration. By vertically stacking multiple shaker screens 508, the footprint of vibratory separator 500 is decreased, thereby providing equivalent separating potential while requiring less space. In vibratory separators 500 using vertically stacked shaker screens 508, the size of the apertures in the screens may be varied according to each tier. As drilling fluid begins to flow from a top tier of vibratory separator 500, the screen assembly apertures may be substantially greater in size than the apertures of lower screen assemblies. To prevent drilling fluid from falling on lower disposed shaker screens assemblies 508, a series of flowback pans 522 may be located under shaker screens 508. Flowback pans 522 may be directed to deposit drilling fluid into a sump 510, thereby allowing drilling fluid to be substantially cleaner at each level of processing.

In this embodiment, vibratory separator 500 also includes a fume hood/outlet 516 connected to housing 502. In one embodiment, the fume hood/outlet 516 may include a vacuum system that extracts vapors into the vent hood/outlet 516. As drilling fluid enters vibratory shaker 500 through inlet end 504, the drilling fluid falls onto shaker screen 508 and is conveyed from inlet end 504 to outlet end 506 using vibratory motion and pulse-assisted screening devices as described above. As the drilling fluid is conveyed, vapors, including potentially hazardous gases, for example, hydrogen sulfide (“H₂S”), entrained in the drilling fluid may be present.

In this embodiment, fume hood/outlet 516 is configured to extract vapors from the drilling fluid as it flows across the shaker screens 508. As vapors and fumes are released in a generally upward direction from the drilling fluid, fume hood/outlet 516 may pull the vapors and fumes inward, thereby trapping the potentially hazardous fumes and/or vapors. Those having ordinary skill in the art will appreciate that by using a fume hood, potentially noxious odors/hazardous conditions may be avoided by directing the flow of air into the hood. Once directed into the hood, a number of subsequent steps may be performed to further treat or vent the trapped gases.

One of ordinary skill in the art will appreciate that fume hood/outlet 516 may be turned on during any step of the separation process including during normal separation, during cleaning, or substantially continuously. Thus, embodiments including fume hood/outlets 516 may provide for a vibratory separator 500 that is substantially enclosed, thereby preventing the escape of hazardous materials and/or vapors into the drilling work space.

In one embodiment, vibratory separator 500 may further include one or more pressure differential devices (not shown) to create a pressure differential between a vapor space 512 above and between the screens 508 and sump 510. In some embodiments, the pressure differential devices (not shown) may be located internal to sump 510. In other embodiments, the pressure differential devices (not shown) may be located external to sump 510. Whether internal or external to sump 510, the pressure differential devices (not shown) may cause vapor to flow from the vapor space between the screens 508 and sump 510 to a point external to sump 510, such as through outlets 54A, 54B (shown in FIG. 3). Fume hood/outlet 516 may be in fluid connection with outlets 54A, 54B to pull vapors that flow through such outlets 54A, 54B, thereby trapping the potentially hazardous fumes and/or vapors. Vapors and fumes trapped in fume hood/outlet 516 may be treated and/or safely removed from vibratory shaker 500 thereafter.

In other embodiments, vibratory separator 500 may include one or more pressure differential devices (not shown) to create a pressure differential between a vapor space 512 above the screens 508 and flowback pans 522. In some embodiments, the pressure differential devices (not shown) may be located internal to flowback pans 522. In other embodiments, the pressure differential devices (not shown) may be located external to flowback pans 522. Whether internal or external to flowback pans 522, the pressure differential devices (not shown) may cause vapor to flow from the vapor space between the screens 508 and flowback pans 522 to a point external to flowback pans 522, such as through outlets 54A, 54B (shown in FIG. 3). Fume hood/outlet 516 may be in fluid connection with outlets 54A, 54B to pull vapors that flow through such outlets 54A, 54B, thereby trapping the potentially hazardous fumes and/or vapors. Vapors and fumes trapped in fume hood/outlet 516 may be treated and/or safely removed from vibratory shaker 500 thereafter.

In one embodiment, after the drilling fluid passes through shaker screens 508, the drilling fluid may be directed to a containment area where the drilling fluid may be degassed to remove remaining entrained gases. Degassing the drilling fluid may be performed by any method known in the art. For example, mechanical degassers and aeration devices may used, as disclosed in U.S. Pat. Nos. 7,727,316 and 7,704,299, assigned to the assignee of the present application, and incorporated herein by reference in their entireties. A mechanical degasser may exert a centrifugal force on the drilling fluid. The centrifugal force of the mechanical degasser multiplies the force acting on the entrained gas (e.g., H₂S) to increase buoyancy of the gas, thereby releasing entrained gas from the drilling fluid. The increase in buoyancy of the gas accelerates the bubble-rise velocity of the gas velocity, and as the gas bubbles rise toward the surface, they escape the drilling fluid. One of ordinary skill in the art will appreciate that any device known in the art that exerts a centrifugal force on the fluid, thereby reducing the amount of entrained or dissolved gases in the process fluid, may be used in place of a mechanical degasser.

Advantageously, embodiments disclosed herein may provide shakers having increased fluid capacity, increased fluid flow-through rates across the screens, and/or improved fluid removal efficiencies. Also, advantageously, embodiments disclosed herein may provide shakers with reduced hazardous vapors in vapor spaces. Finally, embodiments disclosed herein may provide shakers that more efficiently separate entrained gases from drilling fluids.

While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the present disclosure should be limited only by the attached claims. 

I claim:
 1. A method comprising: introducing a slurry to a shaker having a first screen and a second screen; flowing the slurry over the first screen; and applying a first pressure differential to the first screen and not applying the first pressure differential across the second screen.
 2. The method of claim 1 further comprising: applying a second pressure differential to the second screen wherein the second pressure differential is less than the first pressure differential.
 3. The method of claim 1 further comprising: applying a second pressure differential to the first screen wherein the second pressure differential is zero.
 4. The method of claim 1 further comprising: toggling the first pressure differential between static and at least a partial vacuum.
 5. The method of claim 1 further comprising: intermittently interrupting the step of applying the first pressure differential.
 6. The method of claim 1 further comprising: pulsing the step of applying the first pressure differential between the first pressure differential and a second pressure differential wherein the second pressure differential is different than the first pressure differential.
 7. The method of claim 1 further comprising: applying a third pressure differential to a second portion of the first screen.
 8. The method of claim 1 wherein the applying the first pressure differential is generated by a vacuum external to the shaker.
 9. The method of claim 1 further comprising: controlling the air flow under the screen to prevent stalling of the slurry on the screen.
 10. A method comprising: delivering a slurry to a shaker to flow over a first screen and a second screen of the shaker, the slurry having a drilling fluid component and a solids component; generating a first pressure differential between an area above the first screen and an area below the first screen, wherein the pressure differential is created by a device external to the shaker; and applying a second pressure differential to the second screen wherein the first pressure differential is different than the second pressure differential.
 11. The method of claim 10 further comprising: intermittently interrupting the first pressure differential applied to the first screen.
 12. The method of claim 10 further comprising: pulsing the first pressure differential applied to the first screen.
 13. The method of claim 10 further comprising: applying the first pressure differential to a first portion of a second screen.
 14. The method of claim 10 further comprising: conveying vapor and the drilling fluid component from the shaker to a chamber for separation of the vapor from the drilling fluid component.
 15. The method of claim 10 wherein the chamber is a degassing chamber external to the shaker.
 16. The method of claim 10 further comprising: applying vacuum pressure to a portion of the total length of the first screen.
 17. A system comprising: a first screen having an upper side and a lower side for separating drill cuttings and drilling fluid within a shaker; a pressure differential generator configured to pull air or vapor through the first screen to enhance the flow of drilling fluid through the first screen with respect to a second screen within the shaker in which the pressure differential generator does not create a pressure differential between an area above and an area below the second screen; and a chamber in fluid communication with the pressure differential generator and located external to the shaker for collecting the air or vapor and the drilling fluid.
 18. The system of claim 17 wherein the pressure differential generator is located external to the shaker.
 19. The system of claim 17 wherein the air or vapor pulled through the first screen is adjustable to prevent stalling of drill cuttings on the first screen.
 20. The system of claim 17 further comprising: a second pressure differential generator connected to a third screen within the shaker for generating a second pressure differential across the third screen wherein the second pressure differential is different than the pressure differential of the first screen. 